The present invention relates generally to a processing circuit for processing an output signal from a sensing device such as a magnetostriction type torque sensor.
A U.S. patent application Ser. No. 7/969,056 (which corresponds to German Patent Application filing No. P 42 374 16. 2 filed on Oct. 23, 1992) exemplifies a previously proposed detecting and processing circuitry for a sensing device such as a magnetostriction type torque sensor applicable to the detection of a torque of, for example, an output shaft of an internal combustion engine.
In the previously proposed processing circuitry of the torque sensor, a detection of the torque is taken in the form of a change in impedance of detection coils installed on an outer periphery of a magnetostrictive shaft of the torque sensor. However, each impedance in the two detection coils is divided into real parts of the impedances, i.e., iron losses r1, r2 and imaginary parts thereof, i.e., resistances 2.pi.fL1 and 2.pi.fL2 due to inductances of the detection coils. These resistances are temperature dependent not only when the torque is applied about the magnetostrictive shaft but also when the surrounding temperature is changed.
That is to say, since the magnetic characteristic on the magnetrostrictive shaft is changed according to the surrounding temperature, this change being detected in the form of the impedances consisting of the self-inductances and iron losses of the detection coils, a voltage output from a rectifier is deviated from a real value of the torque and is dependent on the temperature, so that an accurate detection of the torque cannot be made.
In addition, the magnetic characteristic described above is different according to a thermal processing of the magnetrostrictive shaft during its manufacture and its magnetic permeability .mu. is different. Consequently, a different magnetic permeability causes an ill effect on a magnetic path resistance (so called, magnetic resistance) which is constituted by the iron losses r1, r2 so that deviations in the sensitivity of each magnetrostrictive shaft occur.